1. Field of the Invention
The present invention relates to an optical fiber ferrule holding plate for an optical fiber end polishing apparatus for simultaneously polishing the optical fiber end surfaces of a plurality of ferrules with optical fibers and, more particularly, to an optical fiber ferrule holding plate for an optical fiber end polishing apparatus which has an improved durability of the section of a polishing holder where the ferrules with the optical fibers are attached and detached and which also has an improved attaching and detaching workability.
2. Description of the Related Art
There have been proposed many optical fiber end surface polishing apparatuses for simultaneously polishing a plurality of optical fiber end surfaces. Takahashi, the inventor of the present invention, has many filed applications for optical fiber end surface polishing apparatuses and has acquired U.S. Pat. No. 4979334 ("Polishing apparatus for end faces of optical fibers") and U.S. Pat. No. 5216846 acquired on Jun. 8, 1993 ("Method and apparatus for grinding foremost end surface of a ferrule").
The aforesaid optical fiber end surface polishing apparatuses are configured to hold an optical fiber ferrule with a plurality of optical fibers thereto in an optical fiber ferrule holding plate, and cause relative movement based on a circular motion between a polishing board and the distal end of the optical fiber ferrule, thereby polishing the distal end of the optical fibers.
The inventor of the present invention has filed an application for "Optical fiber end polishing apparatus for polishing a plurality of types of optical fibers" (Japanese Patent Application No. 6-270529) on a polishing apparatus equipped with an improved optical fiber ferrule holding plate for holding a plurality of optical fiber ferrules with optical fibers attached thereto in order to accomplish a higher operation efficiency of the aforesaid polishing apparatuses.
FIG. 4 is a top view schematically showing the principle of the optical fiber ferrule holding plate which can be used for the optical fiber end polishing apparatus stated above. FIG. 5 is a front cross-sectional view showing a part of the optical fiber ferrule holding plate for the optical fiber end polishing apparatus illustrated in FIG. 4. A cylindrical hub 2 to be coupled to a holding shaft (not shown) is provided at the center of a holder plate main unit 1. A plurality of ferrule fixing sections 3 with optical fibers of the same type are provided on a concentric circle of the holder plate main unit 1.
FIG. 5 is a cross-sectional view taken along section V-V of FIG. 4 showing the details of the ferrule fixing section 3 with a single optical fiber attached. A plurality of FC type ferrules 5 with optical fibers 4 are fixed by the fixing sections 3. End surfaces 6 of the ferrules are pressed against a polishing board 11 at a right angle.
Fixing section 3 includes of a ferrule receiving cylindrical bushing mounting member 8 which includes a through hole 7 through its center. Ferrule 5 is inserted through hole 7. An external screw thread 8a is provided on the outer periphery of mounting number 8. A box nut 9 is provided with a slit 10, and has an internal thread which engages with the external thread 8a so as to tighten and fit the optical fiber and ferrule onto the cylindrical bushing mounting member 8.
Even with the optical fiber ferrule holding plate for the optical fiber end polishing apparatus stated above, in order to polish smaller ferrules, the fixing sections need to be installed densely on the disc, and the slitted box nut 9 and the like must accordingly be made smaller. This has led to a problem in that the box nut 9 or the like may be lost during work. Further installing or removing a single fixing section 3 having the screw thread takes 10 to 20 seconds.
Currently, most optical connector ferrules measure 2.5 mm in outside diameter and 8 mm in effective length. With the increasing trend toward smaller optical circuit systems, however, an optical connector ferrule which is as small as half the size of the aforementioned optical connector ferrule has been developed and is being put to practical use. In such a small optical connector ferrule, the screw-tightening structure is so small that it is difficult to handle. This prevents a ferrule with an optical fiber attached thereto from being fixed to the polishing holder by the conventional screw-tightening method.
Furthermore, the squareness or an error in the tilt angle of the end surface of a polished ferrule with an optical fiber with respect to a central axis seriously affects the connecting performance of the optical fiber connector. The angle of the end surface is known to depend on the gap between the through hole 7 in the mounting member 8 and the outer periphery of the ferrule. If the allowable angle error is taken as 0.2 degree, then the gap has to be designed and manufactured to satisfy one tenth thereof, namely, approximately 0.02 degree. Hence, when the ferrule supporting length of the through hole in the mounting member is 5 mm, the allowable gap is 2 .mu.m in diameter.
Normally, stainless steel which is hardened to about 52 to 60 in Rockwell hardness is used for the material of the mounting member from the aspect of workability. It is practically impossible to completely avoid the adherence of hard diamond or green carborundum powder, which is used as the abrasive, in the gap. It is accordingly impossible to avoid the deterioration in the end surface polishing accuracy over time due to the wear from scratches on the wall surface of the through hole 7 in the fixing section.